Secondary recovery of petroleum

ABSTRACT

This invention relates to the secondary recovery of petroleum, and in particular, involves a process for reducing the amount of water recovered from a producing well in a water flooding process for recovering petroleum from a subterranean oil-bearing formation. This reduction in water is accomplished by introducing a water-in-oil emulsion which contains dispersed therein from 0.01 to 35 percent by weight of a finely-divided water-soluble vinyl addition polymer.

Bott 1March 20, 1973 1 SECONDARY RECOVERY OF 3,336,979 8/1967 Ingraham et a] ..166/295 x PETROLEUM 3,371,712 3/1968 Adams ..166/295 3,373,814 3/1968 Eilers et a1 ..166/295 X [75] Invent Lawrence Oak Park 3,400,761 9/1968 Latimer, Jr. et a1. ..166/294 x Assignee: Nalco Chemical Company Chi ago et al m 3,587,737 6/1971 Tosch ..166 294 [22] Filed: 1971 Primary ExaminerStephen J. Novosad 21 App], 201,439 Attorney-J0hn G. Premo et a1.

' 7 TR [52] US. Cl ..166/295, 166/294 [5 ABS ACT [51] Int. Cl. ..E2lb 33/138 This invention relates to the secondary recovery of [58] Field of Search ..166/294, 295; 175/65, 72; petroleum, and in particular, involves a process for 252/855 A, 8.55 D, 8.5 P reducing the amount of water recovered from a producing well in a water flooding process for [56] References Cited recovering petroleum from a subterranean oil-bearing formation. This reduction in water is accomplished by UNITED STATES PATENTS introducing a waterin-oil emulsion which contains 3,087,543 4/1963 Arendt ..l66/295 dispersed therein from 0.01 to 35 percent by weight of 3,251,414 5/1966 Willman ..l66/295 a finely-divided water-soluble vinyl addition polymer. 3,302,717 2/1967 West et a1 1 ..l66/295 X 3,308,885 3/ 1967 Sandiford ..166/295 8 Claims, N0 Drawings SECONDARY RECOVERY OF PETROLEUM" INTRODUCTION The technique of water flooding to recovercrude, oil from subterranean formations is well known and is described in US. Pat. Nos. 2,827,964and-$399,725. This process involves injecting an aqueous flooding medium into the oil-bearing formation through an input well'penetrating the formation. This provides the energy and flushing action necessary to force; oil

remaining within. the formation into nearby. output wells penetrating the same formation. The efficiency of" such a recovery process will vary with theheterogeneb ty of the formation, i.e., variability in the permeability.

of the formation, and the viscosity of the oil to bedis-J placed.

It has generally been considered uneconomical to employ. water-flooding techniques to recover high viscosity oils. The wide difference between the viscosi-v ty of the residual oil and the viscosity of the water-or brine flooding media results in poor recoveryefficiency. When this difference is great enough an aqueous flooding medium will tend to finger through .thehigh viscosity oil and thereby bypass most of the available oil. The problem of obtaining efficient oilrecoveryis further aggravated by the fact that there are. virtually no oil-bearing formations of uniform permeability.

Rather, the typical oil-bearing formation consists of! multiple layers of rock having differentand:oftenwide:

ly varying permeabilities relative to aqueous or oil liquid flow. There are many pockets or channels in the; subterranean formation. These channels are--merely cracks or disuniformities in the rock: structure. They can be characterizedas being paths of VOl'y iOW fO? sistance to flow.

' In such instances, it is apparent that a floodingmedium will tend to selectively followthe course of least re.- sista'nce, e.g., a zone of high permeability, andithus;

quickly penetrate and bypass the oil. Under theseiadverse conditions, the producing wells'are soon produc:

ing so much of the flooding medium (aqueous solution) in relation to oil that the secondary recovery process-- can no longer be operated economically. Most of these problems have been avoided by the. ad: dition of viscosity-increasing agents to the flooding tivestendto be lost through adsorption on the reservoir rock" surface. As a result ofthis dilution, the blocking or. plugging ability ofthe flooding medium. is diminished until at some. point in the formation the flooding medium has been so diluted that it no longer blocks the channels at all.

Thepresent invention is basedupon'the discovery that awater-in-oil emulsion which contains therein a finely-divided water-soluble vinyl addition polymer can be injected into a producingwell which penetrates the formation, the'result being thatthe channels in the area surroundingthe producing well as well as the inner portionsof the subterranean formation are plugged with a polymeric substance. This phenomenon is due to the fact-that emulsion containing the water-soluble vinyl addition polymer is capable of being invertediin water whereby thewater-soluble vinyl additionpolymer is released'into water as a solution. This results in an uniformly viscous solution throughout the formation without the dilution and adsorption problems of 'the prior art.

The. consequences of this procedure have increased producedoil to water ratios for a certain volume of water. sent through the subterranean formation. Thus,

thetotal amount of water needed to be sent through the formation inorder to produce equivalent volumes of crude oil will bereduced.

OBJECTS lt-isan object of this-invention to increase the oil to waterzratio inthe secondary recovery of oil from subterranean formations.

Italso is an object of this invention to provide a water-in-oil emulsion which-contains dispersed therein a.,flnely-divided water-soluble vinyl addition polymer 1 40 which emulsion-iscapable of beinginvertedin water whereby the water-soluble vinyl addition polymer is released into water as a solution for recovering petroleum-from a subterranean oil-bearing formation.

F urtherobjects will appear hereinafter.

medium. Fatty acid soaps, alginates, sucrose, gl ycerine, carboxymethylcellulose, and water-soluble polymers;

such as polyvinyl alcohols, polyallyl.- alcohols; and hydrolyzed polyacrylamides have been suggestedjfor use as agents in aqueous flooding medium. The. addition of these agents increase the viscosity of the flooding medium. This increased viscosity flooding. mediums.

when injected into the subterranean formation-.atthev input well tends to plug the channels. The fact that the channels of high permeability are blockedresultsinthe;

flooding medium beingforced to pass through the oil.

containing formations, thus increasing the amountofl oil extracted, and resulting in a more runiformrhydroe static face. However, these techniques have been found to be inadequate. The introduction of these-viscosity increasing agents are-quite satisfactory in blockingand; plugging up channels in the initial sections of -thefor-; mation nearest the input well. As thefloodingmedium, is forced further along in the formation ittendstow become diluted by water which is found throughout the formation. In addition, the viscosity-increasing;addi

pumped into. the producing or output well.'Once in the THE INVENTION formation and ,upon contact with the water in the formation. the emulsion is inverted and the polymer released-into solution.

The-water-in-oil emulsion is generally prepared by diluting, a polymeric latex concentratewith-an organic liquid.

The polymeric latex concentrate may be prepared by any number of known techniques. The oils used in preparing these emulsions may be selected from a large group of organic liquids which include liquid hydrocarbons and substituted liquid hydrocarbons.

A preferred group of organic liquids are the hydrocarbon liquids which include both aromatic and aliphatic compounds. Thus, such organic hydrocarbon liquids as benzene, xylene, toluene, mineral oils, kerosenes, naphthas and, in certain instances, petrolatums may be used. A particularly useful oil from the standpoint of its physical and chemical properties is the branch-chain isoparaffinic solvent sold by Humble Oil & Refining Company under the Tradename ISOPAR M." Typical specifications of this narrow-cut isoparaffinic solvent are set forth below in TABLE I:

TABLE I Specification Properties Min. Max. test method Gravity, API at 60/60F 48.0 51.0 ASTM D 287 Color, Saybolt 30 ASTM D 156 Aniline point, F 185 ASTM D 6| 1 Sulfur, ppm 10 ASTM D 1266 (Nephelometric mod.) Distillation, F ASTM D 86 IN 400 410 Dry point 495 Flash point, F(Pensky-Martens closed cup) l60 ASTM D 93 The amount of oil used in relation to the water to prepare the emulsion may be varied over wide ranges. As a general rule, the amount of oil-to-water may vary between 5:1 to 1:10 with preferable emulsions being prepared in the ratio of 1:2 to 1:10. These ratios are illustrative of emulsions that can be prepared, although it should be understood that the invention is not limited thereby.

The emulsions may be prepared by any number of techniques. For example, the emulsions may be prepared by using high speed agitation or ultrasonic techniques. In most instances, however, it is desirable that the emulsion be a stable emulsion and to achieve this end'it is often necessary to employ an oil-soluble emulsifying agent. The amount of emulsifying agent to provide an emulsion will have to be determined by routine experimentation. As a general rule it may be said that the amount of oil-soluble emulsifier may range from 0.1 to 30 percent by weight based on the weight of the oil. To produce stable emulsions the amount of emulsifier will normally be within the range of 12 to percent by weight of the oil.

Rather than provide a listing of suitable emulsifiers, it is preferred to generally recommend as being satisfactory the so-called low HLB materials which are well documented in the literature and are summarized in the Atlas HLB Surfactant Selector. Although these emulsifiers are useful in producing good water-in-oil emulsions, other surfactants may be used as long as they are capable of producing these emulsions. For instance, it has been found that certain high HLB surfactants are capable of producing stable water-in-oil emulsions. A typical low HLB emulsifier is sorbitan monooleate.

DISPERSING THE POLYMERS INTO THE WATER- IN-OIL EMULSIONS In accordance with the first step or procedure of the invention, the water-soluble vinyl addition polymers are dispersed into the water-in-oil emulsion. The polymers as produced by most manufacturing processes are in the form of powders or lump-like agglomerates of varying particle size. It is desirable that the particles, before beingplaced into the emulsion, be comminuted by grinding, abrading or the like so that their average particle size is less than 5 millimeters and preferably is within the range of l to 5 microns. After the powders have been comminuted, they may be dispersed into the water-in-oil emulsion by means of agitation provided by such devices as stirrers, shakers, homogenizers and the like. To be commercially practical, the amount of polymer in the emulsion should be at least 2 percent by weight. The invention contemplates using emulsions containing between 5 to 75 percent by weight with preferred emulsions having a polymer concentration within the range of 10 to 45 percent by weight. In some cases the starting emulsions are converted to suspensions due to the nature andthe amount of the polymer present therein.

The method of preparing a water-in-oil emulsion by the use of a homogenization device is quite simple. Water is added with agitation to an oil-emulsifier mixture to make an emulsion. The finely-divided polymer particles are then added to the emulsion with rapid agitation. The particle size of the polymer should be within the range of 1 micron to about 5 microns. This suspension of polymer particles in the emulsion is passed through a homogenizer. The amount of pressure necessary to produce a smooth emulsion varies in each experiment. The minimum pressure requirement is a function of the abrasiveness of the polymer, the concentration of the polymer and the particle size of the polymer. In general, the pressure requirement is between 1,000 to 3,000 psi. However, depending upon those variables listed, the pressure requirement could be lower or exceed the stated range. A typical homogenizer device is the Manton-Gaulin type.

From a commercial standpoint it is beneficial that the polymer emulsions thus described be stable, yet at the same time contain relatively large amounts of polymers. One method of insuring that the polymers do not precipitate when dispersed in the emulsion is that the particlesize of the polymer be as small as possible. Thus polymers dispersed in the emulsifiers are quite stable when the particle size is within the range of 5 millimicrons up to about 5 microns. To produce particle sizes within these limitations, spray dryers with appropriate size nozzles may be used. It also is possible to prepare the polymer-containing emulsion of the watersoluble vinyl addition polymers directly from the vinyl monomers from which these polymers are synthesized. Such polymer-containing emulsion may be synthesized by using the water-in-oil emulsion polymerization technique set forth in US. Pat. No. 3,284,393. The teachings of this patent comprise forming a water-in-oil emulsion of water-soluble ethylenic unsaturated monomers. The emulsion is formed by utilizing a waterin-oil emulsifying agent. To this monomer is added a free radical-type polymerization catalyst and then heat is applied under free radical-forming conditions to form waterdsoluble polymer latices. The polymeric latex concentrates produced by this patent are relatively unstable and frequently must be treated with additional emulsifiers to render the products stable.

TI-IE WATER-SOLUBLE VINYL ADDITION POLYMERS These polymers are well known to the art and have been described in numerous publications and patents. The polymers most commonly used in many industrial applications are acrylamide polymers which include polyacrylamide and its water-soluble copolymeric derivatives such as, for instance, acrylamide-acrylic acid, and acrylamide-acrylic acid salt copolymers which contain from about 95 to 5 percent by weight of acrylamide. Also useful are copolymers of acrylamide with other vinyl monomers such as maleic anhydride, acrylonitrile, styrene and the like. It is preferred in the practice of this invention to use acrylamide polymers which are water-soluble and which contain at least 5 percent by weight of acrylamide.

A preferred water-soluble vinyl addition polymer of this invention are polyacrylamide. The most preferred polymer is either a copolymer of acrylamide-acrylic acid, having a ratio of 65:35, a copolymer of acrylamide-methacrylic acid having a ratio of 93:7, or a copolymer of acrylamide-dimethylaminoethyl methacrylate (DMAEM) having a ratio of 75:25.

Other water-soluble vinyl polymers are described in detail in the following US. Pat. Nos. 3,418,237; 3,259,570 and 3,171,805.

In examining the disclosures of these patents it will be seen that the water-soluble polymers may be either cationic or anionic and, in some instances, the ionic charges are sufficiently slight so that the polymers may be considered as nonionic.

For example, water-soluble polymers and copolymers of allyl diallyl amines, or dimethylaminoethyl methacrylate are cationic.

Polymers such as polyvinyl alcohol are nonionic, and polymers such as polyacrylic acid or polystyrene sulfonates are anionic. All of these polymers may be used in the practice of the invention.

The molecular weight of the polymers described above may vary over a wide range, e.g., 10,000 to 25,000,000. The invention, however,'finds its greatest usefulness in preparing aqueous solutions or dispersions of these polymers and, in particular, acrylamide polymers whose molecular weight are in excess of 1,000,000. Polymers having higher molecular weights are more difficulty dissolved in water and tend to form extremely viscous solutions at relatively low concentrations. Also, the polymers may be produced by any known methods of conducting polymerization reactions. Thus, solution suspension or emulsion polymerization techniques may be used.

THE ORGANIC LIQUID Generally, the polymeric latex concentrate will be dilutedwith an organic liquid just prior to use. As mentioned above, the preferred polymeric latex concentrationwill have from to 50 percent by weight of a water-soluble vinyl addition polymer. In this application, the polymeric latex concentrate will be diluted with the organic liquid so that the water-in-oil emulsion will have 0.1 to 10 percent by weight of the water-soluble vinyl addition polymer.

The polymeric latex concentrate can be diluted with the organic liquid (including crude oil) near the location of the well where it is to be used. This on-site dilution procedure may be performed in a mixing tank near the well location and then be pumped directly into the well. The organic liquids of thisinvention include both aromatic and aliphatic hydrocarbon compounds. Thus, such organic hydrocarbon liquids are benzene, xylene,

toluene, mineral oils, kerosene, naphthas and petroleurns may be used. In particular, the petroleum recovered from the primary recovery operation (crude oil) may be used to dilute the polymeric latex concentrate for use. The use of petroleum obtained from the primary recovery operation eliminates the burdensome problems in handling other organic liquids but also results in a great decrease in cost.

Oftentirnes it is desirable to use a more concentrated flooding medium than the ones as defined above. If such is the case the polymeric latex concentrate may be used without dilution with an organic liquid. If such is the case the polymeric latex concentrate would be pumped directly into the well without any type of dilution.

In general the polymeric latex concentrate will have a composition as follows:

A. Water ranging between 5 and 25 percent by.

The polymeric latex upon dilution will have a com-- position as follows:

A. Water ranging between 0.1 and 25 percent by weight, I

B. A water-soluble vinyl addition polymer having a concentration between 0.1 and 35 percent by weight;

C. A hydrophobic liquid ranging between 5 and 99 percent by weight;

D. A water-in-oil emulsifying agent having a concentration between 0.001 and 30 percent by weight.

INVERTING TI-IE FLOODING MEDIUM The major discovery upon which this invention is predicated resides in the discovery that when the water-in-oil emulsion of the type described is inverted in the presence of water in the subterranean formation, that the polymer goes into aqueous solution forming an uniformly viscous solution in the formation. The rateat which this occurs may be controlled by the type and an formation. The placement of a surfactant into the flooding medium causes the emulsion to more rapidly invert and release the polymer in the form of an aqueous solution. When this technique is used to invert the flooding medium the amount of surfactant present in the water may vary over a range of from 0.01 to 10 percent based on polymer.

THE SURFACTANTS The preferred surfactants are hydrophylic and are further characterized as being water-soluble. Any hydrophilic-type surfactant such as ethoxylated nonyl phenols, ethoxylated nonyl phenol formaldehyde resin, dioctyl esters of sodium sulfosuccinate, and octyl phenol polyethoxyethanol can be used.

Other surfactants that may be employed include the soaps such as sodium and potassium myristate, laurate, palmitate, oleate, stearate, resinate, and hydroabietate, the alkali metal alkyl or alkylene sulfates, such as sodium lauryl sulfate, potassium stearyl sulfate, the alkali metal alkyl or alkylene sulfonates, such as sodium lauryl sulfonate, potassium stearyl sulfonate, and sodium cetyl sulfonate, sulfonated mineral oil, as well as the ammonium salts thereof; and salts of higher means like lauryl amine hydrochloride, and stearyl amine hydrobromide.

Any anionic, cationic, or nonionic compound can be used as a surfactant.

Following is a list of suitable surfactants that could be used in the practice of this invention. Any watersoluble surfactant could be used, but naturally some are more efficient than others. Useful surfactants in clude, but are not limited to: polyoxyethylene alkyl phenol, polyoxyethylene (10 mole) cetyl ether, polyoxyethylene alkyl-aryl ether, polyoxyethylene monolaurate, polyoxyethylene vegetable oil, polyoxyethylene sorbitan monolaurate, polyoxyethylene esters or mixed fatty and resin acids, polyoxyethylene sorbitol lanolin derivative, polyoxyethylene (12 mole) tridecyl ether, polyoxyethylene sorbitan esters of mixed fatty and resin acids, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyoxyethylene monostearate, polyoxyethylene (20 mole) stearyl ether, polyoxyethylene (20 mole) oleyl ether, polyoxyethylene (15 mole) tridecyl ether, polyoxyethylene fatty alcohol, polyoxyethylene alkyl amine, polyoxyethylene glycol monopalmitate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene mole) cetyl ether, polyoxyethylene oxypropylene stearate,.polyoxyethylene lauryl ether, polyoxyethylene lanolin derivative, sodium oleate, quaternary ammonium derivative, potassium oleate, N-cetyl N-ethyl morpholinium ethosulfate, and pure sodium lauryl sulfate.

In addition to using the water-soluble surfactants described above, other surfactants may be used such as silicones, clays and the like which are included as surfactants since, in certain instances, they tend to invert the emulsion even though they are not water-soluble.

In other specific cases the surfactant may be directly added to the polymer-containing emulsion; thereby rendering it self-inverting upon contact with water. These products, while capable of being used in certain systems, must be carefully formulated since the surfactants may tend to interact with the emulsifier or the emulsion and destroy it prior to its being used.

Other techniques for inverting the emulsions include the use of agitation, heat and pH shift, as well as the placement into the water, into which the polymer-containing emulsion is to be dissolved, certain electrolytes. For any particular polymer-containing emulsion a suitable method for its inversion may be readily determined by routine experimentation.

EXAMPLES When the water-in-oil emulsions are injected into producing wells they have a high water to oil output ratio, generally resulting from many years of secondary recovery operations, it is possible to greatly improve the amount of oil produced in relation to the water recovered.

For instance, when the water-in-oil emulsions would be used to treat typical produced fluid from, for instance, a West Texas water flooding field improvements in the amount of oil produced will range from between 10 to as high as 40 percent by weight.

Specifically, when the water-in-oil emulsions of the invention are used typical results that would be obtained are set forth in Table II below. Typical of the dilutions used are injection fluid which is composed of 95 percent crude oil, 4 percent water, 1 percent polymer. The results shown in Table II would be obtained after continuous injection would be made into the producing wells over a 1-5 week period.

TABLE II Water Ex. (12 by Oil(%) 1: In Increase No. wt) by wt) Polymer Emulsion ln Oil 1 72 28CT Acrylamide 35' 32 2 72 28(l) 93% Acrylamide 7% methaerylic Acid 35 37 3 72 28(T) 65% Acrylamide 35% Acrylic Acid 35 4O 4 67 33(I) 75% Acrylamide 25% DMAEM 3O 20 5 48 52(1) Sodium Poly acrylate 37 20 6 42 58(l) DMAEM 24 15 7 42 58(l) Polystyrene Sulfonate 24 18 l= ISOPAR M T= Toluene DMAEM Dimethyl Aminoethyl Methacrylate While the invention has been described with respect to producing wells of water flooding processes such is intended to include primary production wells which produce crude oil and water.

I claim:

1. A process for reducing the amount of water removed from a producing well used for recovering petroleum from a subterranean oil-bearing formation which comprises introducing a water-in-oil emulsion into a producing well which penetrates said formation, said emulsion containing dispersed therein from 0.01 to 35 percent by weight of a finely-divided water-soluble vinyl addition polymer and which is capable of being inverted in water whereby the water-solublevinyl addition polymer is released into the water as a solution.

2. The process of claim 1 wherein the water-in-oil emulsion is comprised of:

A. water ranging between 0.01 and 25 percent by weight;

percent by weight; and

D. a water-in-oil emulsifying agent having a concentration between 0.1 and 30 percent by weight.

4. The process of claim 1 wherein the concentration of the water-soluble vinyl addition polymer in the polymeric latex is from 0.1 to 10 percent by weight.

5. The process of claim 1 wherein the polymer is an acrylamidesodium acrylate copolymer.

6. The process of claim 5 wherein the weight ratio of acrylamide to sodium acrylate is 65:35.

7. The process of claim 1 wherein the polymer is polyacrylamide.

8. The process of claim 1 wherein the polymer is an acrylamide-methacrylic acid copolymer. 

2. The process of claim 1 wherein the water-in-oil emulsion is comprised of: A. water ranging between 0.01 and 25 percent by weight; B. a water-soluble vinyl addition polymer having a concentration between 0.1 and 35 percent by weight; C. a hydrophobic liquid ranging between 5 and 99 percent by weight; and D. a water-in-oil emulsifying agent having a concentration between 0.001 and 30 percent by weight.
 3. The process of claim 1 wherein the water-in-oil emulsion is comprised of: A. water ranging between 5 and 25 percent by weight; B. a water-soluble vinyl addition polymer having a concentration between 20 and 50 percent by weight; C. a hydrophobic liquid ranging between 5 and 35 percent by weight; and D. a water-in-oil emulsifying agent having a concentration between 0.1 and 30 percent by weight.
 4. The process of claim 1 wherein the concentration of the water-soluble vinyl addition polymer in the polymeric latex is from 0.1 to 10 percent by weight.
 5. The process of claim 1 wherein the pOlymer is an acrylamide-sodium acrylate copolymer.
 6. The process of claim 5 wherein the weight ratio of acrylamide to sodium acrylate is 65:35.
 7. The process of claim 1 wherein the polymer is polyacrylamide.
 8. The process of claim 1 wherein the polymer is an acrylamide-methacrylic acid copolymer. 